What a tough question! They're all so different because of the themes and locations.
I guess if I had to vote I'd have to choose one for the MK area and one for the MGM/EPCOT area (the area we actually prefer).
MGM/EPCOT- I'd have to definitely vote for the Dolphin, a beautiful, amazing atmosphere, great CMs, excellent pool area, even the lap pool is nice because its not real crowded and right in the middle of the magic of EPCOT & MGM not to mention the BW area.
MK- I have to say WL. It just has such a cozy feeling. Even though sometimes you feel you're a little "out there" if you have a car & you valet it's so easy and convenient to get around. Great CMs too. Fun proximatey to FW area.